Hi Aegean,
Offhand, I do not see any specific literature details for water/food process lines. I guess the micro. requirements for potable water represent a logical reference. I would expect yr local Public Heath Department to have such a set of micro. requirements ?
Opinions regarding Legionella action limits for water seem to vary significantly between locations and also with respect to application,eg cooling towers,domestic etc, for example, here is OSHA -
https://www.osha.gov.../otm_iii_7.html
(note the caveat - "Remember that these numbers are only guidelines, and the goal is zero detectable Legionella in a water source.")
and 2 examples for UK -
legionella,2011.pdf 1.26MB
10 downloads
Legionella,2014.pdf 88.3KB
14 downloads
The current UK HSE literature is accessible here -
http://www.hse.gov.u...ns/books/l8.htm
You probably need to find out which reference source is regulatory applicable to yr location.